This invention relates to cooling systems for internal combustion engines, and, more specifically, dynamic cooling systems for internal combustion engines with variable cylinder management.
Internal combustion engines generally require some form of fuel to provide energy for combustion. It is desirable to improve the fuel efficiency of these engines by reducing the engine displacement during times of low load requirements on the engines. Engine displacement is reduced by temporarily suspending operation of some cylinders within the engine. Engine operation with reduced displacement will reduce the amount of fuel consumption compared to engine operation utilizing all cylinders.
The internal combustion process of generating energy for engine operation produces some amount of gaseous byproducts that are carried away from the engine by the exhaust system. In order to properly manage the contaminants present in the combustion byproduct exhaust, the exhaust is treated with a catalytic converter prior to being released to the environment. A catalytic converter includes a catalyst that reacts with the exhaust to reduce the amount of pollutants, such as NOx, expelled in the exhaust. Catalytic converters generally operate most effectively in a certain optimal temperature range. When the exhaust gases entering the catalytic converter either heat or cool the catalytic converter away from the optimal temperature range, the performance of the catalytic converter degrades.
Internal combustion engines, by their nature, generate heat during operation. These engines require temperature regulation of the engine cylinder banks where the combustion occurs to provide for efficient operation and to prevent overheating. Typically, a cooling system is used to regulate the temperature of the engine. In variable cylinder engines, utilization of the cooling system may cause overcooling of the inactive cylinders, thus reducing efficiency of combustion upon reactivating the cylinders that were inactive during reduced displacement. Additionally, cooling of the engine will result in cooling of engine exhaust, which may result in suboptimal operation of the catalytic converter.
In some conventional systems, the cooling system for a multiple-bank engine may be configured such that it cools both banks of engine cylinders in parallel. This provides extremely efficient cooling when both banks of cylinders are firing. However, when one or more banks of cylinders are inactive, a parallel cooling configuration may be less than ideal, as cooling an inactive bank is superfluous. In other conventional systems, the heating and cooling system may be configured in a variable cylinder engine such that the system heats the first cylinder bank in series with the second engine bank. Using this configuration, engine coolant acts to cool first active engine bank and heat the second inactive engine bank during low engine load conditions. Heating the inactive engine bank allows the inactive engine bank begin combusting more efficiently when the load on the engine increases such that it is desirable for all cylinders to fire. However, when all cylinders are firing, series cooling may lead to inefficient or insufficient cooling of the subsequent banks of cylinders.
U.S. Pat. No. 4,436,060 to Tanaka et al., which is hereby incorporated by reference in its entirety, describes heating inactive engine cylinders by heating two engine banks in series. The Tanaka design is suitable for variable cylinder engines during operation in a reduced displacement configuration. In the Tanaka design, the heat extracted from the first engine bank containing actively firing cylinders is transferred to the second engine bank containing inactive cylinders. By transferring heat to the second engine bank, the cylinders remain at a temperature suitable for stable combustion upon reactivation of the cylinders.
The limitation to this design occurs during the full displacement configuration of the engine when all cylinders are actively firing. The engine coolant will efficiently extract heat from the first engine bank, but will have a reduced ability to extract heat from the second engine bank due to the temperature elevation from passing through the first engine bank. As a result, the second engine bank will operate at a higher temperature than the first engine bank. This can lead to damage or increased wear of engine parts sensitive to temperature, such as the fuel valves.
Other solutions to modifying the cooling process of variable cylinder engines are described by Werner et al. in U.S. Pat. No. 7,047,913 and by Watkins et al. in U.S. Pat. No. 2,675,789, both of which are incorporated by reference in their entirety. Both the Werner design and the Watkins design describe reducing the cooling capacity of the engine cooling system during times of reduced displacement operation of the engine. Neither of these designs describe a means for heating the inactive cylinders to improve both fuel efficiency and catalytic converter efficiency.
There is a need in the art for an efficient heating and cooling system for variable cylinder engines that provides the most efficient means of cooling engine during full displacement operation and a means for most efficient heating of inactive cylinders during reduced displacement operation.